rds: switch ->inc_copy_to_user() to passing iov_iter

instances get considerably simpler from that...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/net/rds/recv.c b/net/rds/recv.c
index bd82522..47d7b10 100644
--- a/net/rds/recv.c
+++ b/net/rds/recv.c
@@ -404,6 +404,7 @@
 	int ret = 0, nonblock = msg_flags & MSG_DONTWAIT;
 	DECLARE_SOCKADDR(struct sockaddr_in *, sin, msg->msg_name);
 	struct rds_incoming *inc = NULL;
+	struct iov_iter to;
 
 	/* udp_recvmsg()->sock_recvtimeo() gets away without locking too.. */
 	timeo = sock_rcvtimeo(sk, nonblock);
@@ -449,8 +450,8 @@
 		rdsdebug("copying inc %p from %pI4:%u to user\n", inc,
 			 &inc->i_conn->c_faddr,
 			 ntohs(inc->i_hdr.h_sport));
-		ret = inc->i_conn->c_trans->inc_copy_to_user(inc, msg->msg_iov,
-							     size);
+		iov_iter_init(&to, READ, msg->msg_iov, msg->msg_iovlen, size);
+		ret = inc->i_conn->c_trans->inc_copy_to_user(inc, &to);
 		if (ret < 0)
 			break;